The invention relates to a process for the preparation of polymers of carbon monoxide with one or more olefinically unsaturated compounds.
High molecular weight linear polymers of carbon monoxide with one or more olefinically unsaturated compounds (for the sake of brevity hereinafter referred to as A), in which the monomer units are present in alternating order and which therefore consist of units of the general formula --(CO)--A'--, wherein A' represents a monomer unit derived from a monomer A used, can be prepared by using palladium-containing catalyst compositions.
Depending on the origin of the carbon monoxide used, the above-mentioned polymerization may lead, at otherwise similar reaction conditions, to results which differ widely as to average reaction rates. This may be due to the use of impure carbon monoxide.
The Applicant has made a systematic research into the effect of impurities which may occur in carbon monoxide on the average reaction rate of the afore-mentioned polymerization. It has been found in the first place that some impurities, such as oxygen, hydrogen, carbon dioxide and water, have absolutely no adverse effect on average reaction rates, even when they are present in the carbon monoxide in very high concentrations. For instance, in relation to hydrogen and carbon dioxide, it was established that the polymerization reactions carried out using a carbon monoxide containing 10% vol hydrogen or 15% vol carbon dioxide as impurities could result in the same high average reaction rates as a corresponding experiment carried out using pure carbon monoxide. However, the research has further shown that there are impurities that have an extremely adverse effect on average reaction rates, even when they are present in the carbon monoxide in parts per million by weight (ppmw) quantities. This is the case with sulfur as sulfidic sulfur, such as in carbon oxysulfide, hydrogen sulfide and lower mercaptans and iron as iron carbonyls. In view of the following, this is a highly surprising find. Very attractive catalyst compositions for the preparation of the present polymers are palladium-containing compositions which contain trifluoroacetic acid as one of the components. An earlier investigation carried out by the Applicant into these catalyst compositions has shown that without affecting the average reaction rate during the polymer preparation, the trifluoroacetic acid may be substituted with a sulfur-containing acid, such as paratoluenesulfonic acid or by sulfur-containing salts, such as sulfates of tin, cerium, vanadium, zirconium, chromium or antimony. For instance, the investigation into the catalyst compositions mentioned hereinbefore has shown that the trifluoroacetic acid present therein may be substituted with iron sulfate without any adverse effect on average reaction rates during polymerization.
Accordingly, it has been discovered that the average reaction rate in the afore-mentioned polymerization can be substantially increased when the sulfur and/or iron contents of the carbon monoxide are decreased before the latter is contacted with the palladium-containing catalyst composition.